DE2619877A1 - PROCESS FOR THE POLYMERIZATION OF VINYL CHLORIDE IN AQUATIC SUSPENSION - Google Patents

Description

PAl E N TA N WALTE

DR.A. VAN DERWERTH DR. FRANZ LEDERER REIiMER F.MEYER

DlPL-ING. (1934-1974) DIPL-CHEM. DIPL.-ING.

8000 MUNICH 80

LUCILE-GRAHN-STRASSE 22

TELEPHONE: (089) 472947 TELEX: 524624 LEATHER D TELEGR .: LEATHER PATENT

Munich, March 23, 1976 Pp. 75/10

SOLVAY & CIE.

33 »ue du Prince Albert, Brussels, Belgium

Process for the polymerization of vinyl chloride in aqueous

suspension

The invention relates to a process for the polymerization of vinyl chloride in aqueous suspension, which results in polymers leads, which have improved initial heat stability, and in particular a process in which the polymerization in the presence of dialkyl peroxydicarbonates used as initiators is carried out.

Dialkyl peroxydicarbonates are known to be particularly active initiators. Therefore, they have the advantage of increasing productivity of polymerizers increase. Unfortunately, however, the polymers they result in give shaped articles such as pipes, cable windings and bottles, their initial heat stability leaves a lot to be desired.

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The initial heat stability is the ability of the polymer to withstand degradation caused by the increase in temperature that it is necessary to incorporate the various additives and must be subjected to its processing. Poor initial heat stability is reflected in a change the initial color, which is greater, the smaller the Stability is.

It has already been proposed to improve this stability by an aftertreatment after the polymerization consists of bringing the polymers into contact with an aqueous, alkaline solution, which is preferably a phenolic Contains antioxidant, see Canadian Patent 865 802. The vinyl chloride polymers which have been subjected to such a treatment have a slightly improved heat stability for certain, very special approaches, e.g. B. those with tin. However, for many approaches this is the initial heat stability generally less good than that of polymers which have not undergone the treatment. This treatment therefore has only a very limited effectiveness and a very limited application.

The object of the invention is a noticeably more effective treatment method, about the initial heat stability of vinyl chloride polymers to improve, which were polymerized in suspension with the aid of dialkyl peroxydicarbonates, this Treatment process should have a practically general applicability, whatever that for the use of the polymer approach used is.

The invention therefore relates to a process for the polymerization of vinyl chloride, in which the vinyl chloride in aqueous The suspension is polymerized with the aid of dialkyl peroxydicarbonates and the polymer is mixed with a hydroxide

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which is characterized by the fact that the treatment of the polymer is carried out with a monobasic hydroxide at the end of the polymerization, before the unconverted Vinyl chloride is removed.

Surprisingly, it has been found that to improve the initial heat stability of the polymers in question in it is significantly necessary that the treatment by the hydroxide is carried out at the end of the polymerization, when the desired degree of conversion is achieved.

Generally, the polymerization is stopped after approximately 90 to 95% of the vinyl chloride present in the reaction vessel has been converted. At this point in time there is therefore still 5 to 10 % unconverted vinyl chloride present. Typically, a substantial part of this unconverted vinyl chloride is removed from the aqueous suspension by volatilization, which is brought about by means of a reduction in pressure. This process is also known as "blowing off". At the end of the blow-off, the medium contains in the order of magnitude only 10 g of unconverted vinyl chloride per 1 kg of the polymer. Most of the remaining vinyl chloride is trapped inside the polymer particles. It has been found by the applicant that the use of the hydroxide before the end of the blow-off tends to greatly improve the effectiveness of this treatment. The treatment is preferably carried out when the aqueous suspension still contains at least 25 g of unconverted vinyl chloride per 1 kg of polymer. The best results are obtained when this content is at least 50% vinyl chloride per 1 kg.

The treatment according to the invention can be carried out very simply by adding the hydroxide directly to the aqueous suspension

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this is still in the polymerization reactor "is carried out will.

The amount of hydroxide to be introduced into the aqueous suspension is not critical. The introduction of small amounts of Hydroxide already makes it possible to improve the initial heat stability of the polymer. However, it is preferred to use a sufficient amount of hydroxide to bring the pH of the aqueous suspension to a value at least equal to 7 bring. It is also preferred not to exceed a pH value of 12 in the course of the treatment in order to avoid any risk degradation of the polymer, e.g. B. by elimination of hydrogen chloride to avoid. It is preferable to use a kenge of alkali hydroxide, which is sufficient to bring the pH of the aqueous suspension to a value between 9 and 10.5.

The type of monobasic hydroxide used is not critical. It can be made from the hydroxides of alkali metals, such as Sodium hydroxide, potassium hydroxide and lithium hydroxide, as well as ammonium hydroxide can be selected. The term "alkali hydroxide" therefore also includes ammonium hydroxide. The water-soluble alkaline earth metal hydroxides are, however, for the present invention Procedure not suitable.

A particularly preferred alkali hydroxide is ammonium hydroxide. This hydroxide is found because of its increased volatility not in the finished polymer. Its use ensures the production of polymers covering a whole range of have very desirable properties, namely not only excellent initial heat stability but also excellent increased transparency and good electrical properties.

The way in which the hydroxide is introduced is also not critical. It can, for example, in the aqueous suspension

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can be introduced all at once, in portions, or continuously. The hydroxide can also be in solid form or in solution in a PliJsai.p-lr.c-t which is inert under the polymerization conditions to be introduced. It is even possible to introduce ammonia. The hydroxide is preferably introduced into the aqueous suspension in the form of a solution and especially in the form of an aqueous solution. The concentration of the aqueous hydroxide solution can be arbitrary. However, for practical reasons, solutions between 0.1N and 10N are generally used, and preferably Solutions from 1 IT to 5 N.

According to a particularly preferred embodiment of the invention, the aqueous suspension of the polymer is therefore treated prior to total blow-off with ammonium hydroxide in sufficient quantity to bring the pH to a value between 9 and 10.5 bring. This goal is achieved under the usual conditions for the polymerization of vinyl chloride in aqueous suspension using an amount of ammonium hydroxide that is approximately 0.05 to 1 part by weight of ammonia per 100 parts by weight of starting used · corresponds to vinyl chloride.

The duration of the treatment according to the invention is not critical. In practice, advantageous values can be achieved after just a few minutes Results. These results can be improved by increasing the duration of the treatment. However, to get the full In order not to unnecessarily extend the cycle of polymer production, the polymer is generally kept with the alkali metal hydroxide for about 5 "to. before completely blowing off 120 minutes and preferably for about 5 to 20 minutes in Contact.

The temperature at the time of the start of the treatment according to the invention is usually that of the aqueous suspension at the end of the polymerization as the treatment will be carried out

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as soon as the desired degree of conversion has been achieved. However, it is not absolutely necessary to keep the temperature constant during the course of the treatment. It can therefore be decreased or increased, and in general it is between 20 and 140 ^° C. and preferably between 20 and 80 ^° C.

In addition, it is not strictly necessary treatment to be carried out with stirring or stirring. However, to ensure rapid and effective dispersion of the hydroxide inside to ensure the aqueous suspension of the polymer and thus shorten the treatment time as much as possible it is advantageous to carry them out with stirring or stirring. In practice, therefore, during the time according to the invention Treatment run the agitator used during the polymerization process when the treatment is in the polymerization reactor is carried out.

According to a preferred embodiment of the invention After the treatment with the monobasic hydroxide, the polymer is subjected to an entrainment treatment by a method subjected to inert fluid.

Such treatment is in the Luxembourg patent applications 7O73S of August 14, 1974 and 72112 of March 21, 1975 by the applicant described. The applicant has found that by combining the treatment according to the invention with an entrainment treatment the initial heat stability of the polymer is significantly improved by an inert fluid.

The inert fluid entrainment treatment is common carried out on the aqueous suspension of the polymer, which was brought to a temperature which is at least the Polymerization temperature is the same. This kit dragging treatment is preferably carried out at a temperature which

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at least the freezing temperature or the freezing range of the polymer is the same. If you have the dragging combined with the treatment according to the invention, a blow-off or is preferably carried out before the entrainment treatment a degassing of the aqueous suspension by such that most of the vinyl chloride, which is in the aqueous Suspension at the end of the hydroxide treatment is removed will. The main effect of the entrainment treatment is to remove the last traces of vinyl chloride in the polymer particles are included.

As with the treatment with hydroxide, the entrainment treatment can be used be carried out in the polymerization reactor. However, you can also use another one specially designed for this purpose Use a container which is preferably equipped with a metering device. The polymer is in the form of the aqueous suspension transferred, e.g. B. after a blow-off process carried out in the reaction vessel. You can also do this before dragging change the concentration of polymer in the aqueous suspension. However, preference is given to carrying out the method according to the invention Treatment in the polymerization reactor, then transfers the aqueous suspension of the polymer into a special one Container where a blow-off and the entrainment treatment with an inert fluid are carried out if necessary.

Under the expression "inert Fluid "are the inert gases such as nitrogen and carbon oxide or also vapors from inert gases and at the temperature of the entrainment treatment volatile liquids such as B. pentane, hexane, chloroform, carbon tetrachloride and water to understand. It is particularly advantageous to use steam as the inert fluid for the entrainment treatment. You can at least part of the water vapor serving as the fluid for the entrainment treatment

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Generate in situ by bringing the aqueous suspension to the boil will.

However, it is preferred to introduce steam, preferably superheated steam, into the aqueous suspension.

The temperature at which the entrainment treatment with an inert fluid is carried out can be of the same order of magnitude as applied to the hydroxide treatment. However, as previously described, it is particularly advantageous, the entrainment treatment with an inert

perform the th fluid at a temperature that is at least the freezing temperature or the freezing range of the polymer is the same. To determine the freezing temperature or the Freezing range, differential thermal analysis is advantageously used, which gives sufficiently accurate values.

Kan can therefore use the aqueous solution derived from the hydroxide treatment Heat the suspension in order to bring it to a temperature which is at least the freezing temperature or the freezing range of the Polymerisates is the same before the entrainment treatment is subjected to by the fluid. This heating of the aqueous Suspension can be carried out in any suitable manner, for example by circulating heating fluid in a jacketed jacket of the container in which the aqueous suspension is kept and / or by blowing in a hot, inert one directly Fluids, e.g. from air, nitrogen or water vapor. However, the injection of steam is preferred. The usage of Steam enables the desired temperature to be reached in extremely short periods of time.

The upper limit for the temperature at which the entrainment treatment can be carried out with an inert fluid, is determined by the temperature of the breakdown of the polymer,

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to which a customary heat stabilizer can optionally be added can.

It should be pointed out, however, that heating to elevated temperatures, in particular above 100 ^° C., is a useless waste of energy. In addition, an aqueous suspension treated at an elevated temperature must then be cooled before it could be centrifuged off or sucked off, whereby the duration of the cooling and / or the volume of the cooling fluid required were increased.

For these reasons it is preferred not to exceed the aqueous suspension to a temperature 140 ⁰ C and preferably 120 ⁰ C, the inert during the Mitschleppbehandlung by ·! To hold fluid.

The temperature of the entrainment of the remaining monomer and, if necessary, of the previous heating of the aqueous Inert fluids used in suspension can be any. It goes without saying, however, that the total duration of the The higher the temperature of the fluid used for heating, the shorter the treatment of aqueous suspensions lies.

The duration of the entrainment treatment does not represent either critical parameter.

It follows from this that it can be determined in a simple manner by experiments for each particular case. As a hint it should be noted that a few minutes up to about two hours and particularly advantageously 5 "to 45 minutes are generally sufficient, the residual vinyl chloride content to a few tens of parts per million (ppm) expressed by weight on the polymer. Deliver such suspensions

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after centrifuging or spinning off and drying under normal conditions vinyl chloride polymers, which contain less than 2 parts per million by weight of residual monomer in most cases.

Finally, it can be advantageous to conclude the entrainment treatment with a fluid by lowering the pressure a boiling of the aqueous suspension is caused.

The polymerization conditions of those treated according to the invention Polymers are the classic conditions which underlie the polymerization of vinyl chloride in aqueous suspension Use of dialkyl peroxydicarbonates can be applied.

Under polymerization of vinyl chloride is both the homopolymerization as well as the copolymerization of vinyl chloride with comonomers. The content of the polymer is preferably of vinyl chloride above 50 mol% and particularly preferred above 80 mol%. The comonomers can be selected from the monomers copolymerizable with vinyl chloride, z. B. from vinyl acetate, propylene and ethylene.

The polymerization of vinyl chloride is carried out in the presence of the usual constituents for the polymerization in aqueous suspension, i.e. suspending agents and, if appropriate, various additives that are added at any point in the polymerization, such as stabilizers (e.g. epoxidized soybean oil), plasticizers (eg. B ₃ dialkyl), various dyes and pigments, reinforcing agents (eg. B. methacrylonitrile-butadiene-styrene resins) _s the processing facilitating agents (eg. as stearic acid or fatty alcohols), or antioxidants such as Tliioäthern, organic phosphites or phenolic compounds «Examples of such compounds are: phenol, bisphenol-A,

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Hydroquinone, p-tert.-butylcetechol, p-tert.-butylcresol, Tri s- (2-methyl-4-hydroxy-5-tert-buty-phenyl) -butane, n-octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, etc.

Because of their inhibiting effect on the polymerization, the antioxidant compounds are optionally in the aqueous suspension is preferably introduced at the end of the polymerization before the unconverted vinyl chloride is removed will. It is advantageous to add them to the polymerization medium precede treatment with a monobase hydroxide according to the invention.

The suspending agent can be selected from the usual suspending agents be selected, e.g. B. polyvinyl alcohols, gelatin, alkyl celluloses and water-soluble carboxymethyl cellulose ^ as well as from various copolymers and condensation products such as B. the products resulting from the condensation of polyalkylene glycols and polyamines. Of course you can one also continues to use mixtures of suspending agents the way they are introduced is not critical.

Otherwise, all alkylene peroxydxcarbonates are used as initiators suitable for the polymerization of vinyl chloride according to the process according to the invention. These initiators correspond to the following general formula:

ROCOOCOR ¹

Il It

0 0

wherein R and R ^{1 represent the} same or different aliphatic radicals which are optionally substituted, e.g. B. substituted by halogen atoms can be. However, the use of long alkyl chain peroxydicarbonates, which are generally solid, can cause dosing or dosing difficulties

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Handling and transportation. to lead. For this reason, it is preferred to use dialkyl peroxydicarbonates, their alkyl chains having no more than 9 carbon atoms and preferably from 1 "to 4 carbon atoms. A particularly preferred one Peroxydicarbonate is diethyl peroxydicarbonate.

Incidentally, there is an improvement in the heat stability of vinyl chloride polymers most pronounced when applying the process of the invention to the polymerization of vinyl chloride in the presence of dialkyl peroxydicarbonates, the alkyl radicals of which have 1 to 9 carbon atoms and preferably 1 to 4 carbon atoms exhibit.

They treated according to the process of the invention vinyl chloride polymers can be used for all classic applications for such polymers. You are special for use in approaches that are critical with regard to the initial heat stability and under severe operating conditions suitable. The polymers that have also been subjected to an entrainment treatment with a fluid and that are practical contain no more residual vinyl chloride, are particularly good for the production of packaging for food or Suitable for food.

The invention is explained in more detail using the following examples, this being based on the polymerization of vinyl chloride in aqueous suspension in the presence of used as an initiator Obtain diethyl peroxydicarbonate.

The heat stability at short times (initial color) of the polymers was determined at a PEII obtained by kneading at 1.80 ⁰ C for approximately 2 minutes on a roller mixer at the three following compositions:

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Table I. Composition in weight

dry resin dioctyl phthalate tribasic lead sulfate Lead stearate barium cadmium stabilizer "basic lead carbonate Calcium carbonate polyethylene wax stearic acid

100

40

0.5

0.5

100
30th

0.5

100

0.5 1.03

0.6 0.2

example 1

In an autoclave with a capacity of 3 liters, equipped with a stirrer and a jacketed jacket, 150 g of demineralized water, 1.2 g of polyvinyl alcohol and 0.35% of diethyl peroxydicarbonate were introduced at ambient temperature and with stirring (200 rpm). The autoclave was sealed, the stirring was switched off and the autoclave was placed under a partial vacuum of 100 mm Hg, then a nitrogen purge (600 mm Hg absolute) was carried out in the autoclave before placing it again under the same partial vacuum. Then, 1000 g of vinyl chloride were introduced herein · With stirring (500 rpm) was started again, and the medium was heated to 60 ⁰ C. This point in time at which the polymerization starts is regarded as the beginning of the complete polymerization cycle.

After 3 hours, 300 g of demineralized water were introduced, and the polymerization was continued until the

Pressure drop in the autoclave had reached 3 kg / cm. To this

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At this point, 172 cm ^ of a 0.1 N solution of ammonium hydroxide are obtained was introduced into the reactor and stirring was maintained for 10 minutes.

After this period of time, the aqueous suspension was reduced by lowering of the pressure "absolutely blown off or degassed up to 500 mm Hg, the polymer was spun off and dried under the usual conditions, namely 65 ° C. for 2 hours.

The initial heat stability of the polyvinyl chloride obtained in this way in batches A, B and C is given in Table II below. The freezing range, determined by differential thermal analysis, amounts to 80 ^° C.

Example 2 (comparative example)

This example relates to the polymerization of vinyl chloride under the same conditions as in Example 1. As soon as the

ο
The pressure drop in the reactor had reached 3 kg / cm, the aqueous suspension was blown off or degassed, centrifuged and the polymer was ^{dried at 65 °} C. for 2 hours.

The initial heat stability of the polyvinyl chloride thus obtained in batches A, B and G is also given in Table II.

Example 3

The conditions of the polymerization and the treatment of the aqueous suspension with ammonium hydroxide were the same as those from Example 1. However, xv was made after blowing off or degassing the degassed, aqueous suspension in a container of 7? 5 1 transferred, the ax was equipped with a steam supply pipe, which was immersed in the container kept under atmospheric pressure. A sample of the aqueous suspension was taken, to determine their vinyl chloride content. This amounted to

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to 12,000 mg vinyl chloride per kg of polyvinyl chloride. ^{Steam superheated to 152 °} C. was introduced into the aqueous suspension through the immersion tube. The aqueous suspension, which was initially at about 60 ^° C., heated up rapidly in contact with the steam which condensed therein. Once the aqueous suspension had reached! Temperature of 100 ⁰ C (boiling temperature), the water vapor not condensed practice more and escaped right under entrainment of residual vinyl chloride. The supply of superheated steam was stopped after, the aqueous suspension was maintained for 15 Hinuten to 100 ⁰ C under entrainment with water vapor, and it has a second sample of the aqueous suspension prior to cooling, centrifuging and drying the polymer. After the entrainment treatment with steam, the vinyl chloride content of the aqueous suspension was 10 mg of vinyl chloride per kg of polyvinyl chloride, and the dry polymer contained less than 1 mg of vinyl chloride per kg of dry polymer.

The initial heat stability of this polyvinyl chloride in the Runs A, B and C are given in Table II below.

Example 4 (comparison example)

This example was carried out according to the procedure of Example 1 performed except that the treatment with ammonium hydroxide was carried out after blowing off or degassing the aqueous suspension.

The initial heat stability of the polyvinyl chloride in the approaches A, B and C are also given in Table II below.

Example 5 (comparative example)

This example relates to the polymerization of vinyl chloride under the operating conditions of Example 2, but with the degassed or blown, aqueous suspension of an entrainment treatment with steam among those described in Example 3

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Was subject to conditions.

The initial heat stability of the polyvinyl chloride is given in Table II below.

The comparison of Example 1 with Examples 2 and 4- shows that the alkaline treatment of the aqueous suspension prior to blowing or degassing the initial color of polyvinyl chloride resins (Example 2) significantly improved, and this also significantly more than with a working method according to the prior art of technology (Example 4-).

Example 3 shows that the initial heat stability improves can be when the treated according to the invention, aqueous suspension of entrainment treatment by an inert Fluid is subjected.

Finally, Comparative Example 5 shows that the from Improvement of the initial heat stability resulting from an alkaline treatment according to the invention, that with an entrainment treatment connected by an inert fluid (Example 3) shows better results than would have been expected (Examples 1 and 5).

The alkaline treatment of the aqueous suspension before blowing off or degassing is therefore a particularly effective and simple means of preventing the initial coloration of polymers from vinyl chloride to improve.

In addition, this alkaline treatment is obtained according to the invention with entrainment of the remaining monomer connects by an inert fluid, vinyl chloride polymers, which have an even better initial color and practically free of residual monomers! are.

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Example 6

The procedure of this example corresponds to that of Example Λ with the exception that before introducing the ammonium hydroxide solution, 0.5 g of tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane dissolved in 0.5 g of dichloromethane , were injected.

The initial heat stability of the polyvinyl thus obtained chi ο rid it in approaches 4, B and C is also in the given in Table II below.

Table II

E.g. Initial heat stability of ketched skins B. C. A. very light pink beige 1 White deep pink + number
rich red dots Brown 2
(Cf. pink + some
) Red dots not colored light beige 3 White deep pink Brown 4th
(Cf. reddish + red
) Points pale red deep beige (Cf. pink
) very light pink light beisre 6th White

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Claims (20)

Claims 1./Process for the polymerization of vinyl chloride, whereby ' the vinyl chloride is polymerized in aqueous suspension with the aid of dialkyl peroxydicarbonates and the polymer is treated with a hydroxide, characterized in that the polymer is treated with a monobasic hydroxide at the end of the polymerization, before the unconverted vinyl chloride is removed. 2. The method according to claim 1, characterized in that there is used such an amount of monobasic hydroxide that the pH of the remaining suspension is at least 7. 3. The method according to claim 1, characterized in that such a quantity of hydroxide used monobasic _r that the pH value of the aqueous suspension does not exceed 12th 4. The method according to any one of claims 1 to 3 »characterized in that that one uses such an amount of monobasic hydroxide that the pH of the aqueous suspension is between 9 and 10.5. 5. The method according to claim 1, characterized in that one used as monobasic hydroxide ammonium hydroxide, lithium hydroxide, potassium hydroxide or sodium hydroxide. 6. The method according to claim 5, characterized in that ammonium hydroxide is used as the monobasic hydroxide » 609851/0952 7. The method according to claim 1, characterized in that dae monobasic hydroxide is used in the form of an aqueous solution. 8. The method according to any one of claims 1 to 7> characterized in that an aqueous suspension is treated which still contains at least 10 g of vinyl chloride per 1 kg of polymer. 9. The method according to any one of claims 1 to 8, characterized in that that the duration of the treatment of the aqueous suspension with the monobasic hydroxide between 5 minutes and 120 minutes. 10. The method according to any one of claims 1 to 9 _5, characterized in that an antioxidant is added to the aqueous suspension. 11. The method according to claim 10, characterized in that the antioxidant entered at the end of the polymerization before removing the unconverted vinyl chloride. 12. The method according to any one of claims 1 to 11 ,. characterized, that the addition of the antioxidant takes place before the treatment of the polymer with a monobasic hydroxide. 13 · The method according to claim 10, characterized in that used a phenolic compound as an antioxidant. 14. The method according to claim 1, characterized in that the treated with the monobasic hydroxide, aqueous suspension subjected to an inert fluid entrainment treatment. 609851/0952 15 · The method according to claim 14, characterized in that water vapor is used as the inert fluid. 16. The method according to claim 14, characterized in that the "treated, aqueous suspension before carrying out the Entrained) action blows off or degassed. 17. The method according to claim 14, characterized in that the treated, aqueous suspension is heated to a temperature, which is at least equal to the freezing range of the polymer, and that it is at a temperature which is at least equal to the freezing range of the polymer, in the course of the entrainment treatment by a holds inert fluid. 18. The method according to claim 1, characterized in that the polymer with ammonium hydroxide in such an amount treated that the pH of the suspension is between 9 and 10.5, while the aqueous suspension is still at least Contains 25 g of vinyl chloride per 1 kg of polymer. 19 · Method according to one of claims 1 to 17 »characterized in that that you apply it to aqueous suspensions of polymers of vinyl chloride, which with Zuhilfeahrce of dialkyl peroxydicarbonates, their alkyl chains 1 to 9 Containing carbon atoms have been polymerized. 20. The method according to claim 19, characterized in that the Alkyl chains have 1 to 4 carbon atoms. 609851/0952